My 95 RR Classic had a catastrophic brake fail. All the fluid from the reservoir emptied out thru the seals & onto the exhaust manifold creating a fire, which was extinguished within a minute. I replaced the reservoir bottle & seals, DOT 4 fluid, bled the brakes to the letter with ignition on according to RAVE manual. I still can not get any pressure the rear calipers.
Replacement Master Cylinders are not east to find, so is a rebuild of mine the only option???
Thank you, be well stay safe

Try this ....
Take a length of vacuum hose that will fit on the bleeder nut on the caliper... insert the hose into a bottle of brake fluid... about half full with the hose going to the bottom... loosen The bleeder nut and put the hose
On the nut...
Then when you pump the brakes... as the air goes out the brake lines..the fluid will suck back into the brake lines... just keep the Reservoir full...this is the self bleed method
Start with the farthest wheel from the fluid reservoir...
It takes a little time and patients
But... it works

Or see if you can hire a bleed kit, the one that fits to the spare tyre, giving extra pressure ...

This one is available from various places ...



Has fluid held in separate container ...

https://www.carbibles.com/best-brake-bleeder-kit/